US5370000A - Magnetic flowmeter with fault detection - Google Patents

Magnetic flowmeter with fault detection Download PDF

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Publication number
US5370000A
US5370000A US07/906,507 US90650792A US5370000A US 5370000 A US5370000 A US 5370000A US 90650792 A US90650792 A US 90650792A US 5370000 A US5370000 A US 5370000A
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Prior art keywords
signal
differential amplifier
output
input
signals
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Expired - Fee Related
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US07/906,507
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English (en)
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Jorg Herwig
Dieter Keese
Karl H. Rackebrandt
Hans W. Schwiderski
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Fischer and Porter Co
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Fischer and Porter Co
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Assigned to FISCHER & PORTER GMBH reassignment FISCHER & PORTER GMBH ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: HERWIG, JORG, KEESE, DIETER, RACKEBRANDT, KARL H., SCHWIDERSKI, HANS W.
Assigned to FISCHER & PORTER COMPANY reassignment FISCHER & PORTER COMPANY ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: FISCHER & PORTER GMBH
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/56—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects
    • G01F1/58—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects by electromagnetic flowmeters
    • G01F1/60—Circuits therefor

Definitions

  • the present invention relates to a circuit to detect disturbances in a magnetic flowmeter flow measurement system.
  • This circuit is of this type which responds to disturbances in the system ahead of the measuring circuit and, in particular, to the isolation of at least one input to the measuring circuit.
  • Such an isolation of the input of the measuring circuit can result if an insulating layer is deposited on the corresponding electrode by the metered fluid, or the connection to the corresponding electrode is broken, or if, in any other manner, the electrically conductive path between the reference potential and the fluid is disturbed.
  • Magnetic flowmeter fault detection apparatus constructed in accordance with the present invention, includes a pipe through which fluid flows and means for generating a magnetic field which extends through the pipe. Also included in this apparatus are first and second electrodes for developing first and second signals, respectively, representative of fluid flowrate through the magnetic field. The apparatus further includes means for:
  • FIG. 1 shows a first embodiment of a circuit constructed in accordance with the present invention.
  • FIG. 2 shows a second embodiment of a circuit constructed in accordance with the present invention.
  • FIG. 3 shows a curve with the diagnostic time intervals and the measurement time intervals when a bipolar magnetic field exists.
  • FIG. 4 shows a curve with the diagnostic time intervals and the measurement time intervals when a bipolar sinusoidal magnetic field exists.
  • FIG. 5 shows a curve useful to explain the operation for saturation.
  • FIG. 6 shows a third embodiment of a circuit constructed in accordance with the present invention.
  • FIG. 7 shows a fourth embodiment of a circuit constructed in accordance with the present invention.
  • the flow measuring circuit designs shown in FIGS. 1 and 2 include a meter pipe 1.
  • a magnetic field, generated by coils 2,3, extends perpendicularly through pipe 1.
  • An excitation current I EER passes through the coils 2,3 which are connected in series, although they could also be connected in parallel.
  • Electrodes 4,5 are installed on opposite sides of the meter pipe 1 perpendicular to the longitudinal axis of the magnetic field. A voltage, essentially proportional to the flowrate of the flowing fluid, is present on the electrodes 4,5.
  • the electrodes 4,5 are connected by leads 6,7 to the inputs of the impedance converters 8,9, which have a relatively high input impedance and a relatively low output impedance, and are located in close proximity to the electrodes 4,5.
  • the outputs of the impedance converters 8,9 are connected by leads 10,11 to terminals 12a,13a, respectively, of bipolar switch 12/13.
  • the other terminals 12b,13b of bipolar switch 12/13 are connected to the reference potential.
  • the output of the switch 12/13 is connected by leads 14,15 to the two inputs of the signal amplifier 16.
  • the output of the signal amplifier 16 is connected by lead 17 to the multiplexer 18.
  • the output of the multiplexer 18 is connected to an input of the A/D converter 20.
  • the output of the A/D converter 20 is connected by lead 21 to an input of the microprocessor 22.
  • the microprocessor 22 controls, through lead 31, the multiplexer 18 and, through leads 32 and 33, the switches 12 and 13 of bipolar switch 12/13
  • outputs of the microprocessor 22 are connected by lead 23 to a alpha-numeric LCD-display 24, by lead 25 to a current output circuit 26 for connection by lead 27 to an optional totalizer, by lead 28 to a binary pulse output circuit 29 for connection by lead 30 to an optional binary pulse device, and by lead 34 to optocoupler pulse out circuit 35 for connection by lead 36 to an optional optocoupler device.
  • the switches 12 and 13 are controlled through leads 32 and 33, which either set both switches in the mode shown in FIG. 1 or set the one switch 12 or the other switch 13 through the terminals 12b or 13b to the reference potential or set both switches 12 and 13 through terminals 12b and 13b to the reference potential.
  • the signal voltages from the electrodes 4 and 5 are the same but with opposite polarity.
  • the signal voltage at the output of the impedance converter 8 has an amplitude +U S and the signal voltage at the output of the impedance converter 9 has an amplitude -U S .
  • An amplified signal U k (2 U S ), where k is a proportionality factor, exists on the output of the signal amplifier 16. This amplified signal is only used during the measurement time intervals TM (see FIG. 3).
  • the switch 13 is connected to the reference potential by terminal 13b.
  • the switch 12 is connected to the reference potential by terminal 12b.
  • both switches 12 and 13 are connected to the reference potential by terminals 12b and 13b.
  • the total time duration of the diagnostic time intervals T2, T3, and T4 is TD.
  • the output signal from the signal amplifier 16 during the diagnostic time intervals T2 and T3 is one-half the amplitude of the signal U, i.e. 1/2 U.
  • These signals are converted into digital signals in the A/D converter 20 and evaluated by the microprocessor 22 and designated as "error free".
  • the microprocessor can recognize if electrode 4 or electrode 5 or both electrodes 4 and 5 are coated with an insulating layer or if some other disturbance has occurred in the connections between the inputs of the switches 12 and 13 and the reference potential.
  • FIG. 5 shows schematically the variation of the output signal of the signal amplifier 16 during normal operation between +kU S and -kU S and the appearance of a disturbance signal in the diagnostic time interval T3 at the time t St .
  • the signal jumps (e.g. to U max ).
  • the polarity of the signal at time t St can not be determined, thus the signal jumps either to U max or U min .
  • the microprocessor 22 will also recognize a large disturbance signal on top of the signal from the signal amplifier 16.
  • the microprocessor 22 can also recognize this fact. For the same reason, the microprocessor 22 can also recognize differences in the noise content of the electrode signal due to a different build up on each of the electrodes 4 and 5, especially before a complete electrode signal loss occurs.
  • the fluid is connected to the reference potential through grounding rings installed at the ends of the insulated pipe 1.
  • the microprocessor 22 will recognize if the grounding rings are coated with an insulating layer.
  • the microprocessor 22 will also recognize if one the leads 6 or 7 is broken or if both leads 6 and 7 are broken, and also if an electrically conductive path exists between at least one of the electrodes 4 and 5 and the reference potential or whether an electrically conductive path exists between at least one of the leads 6 and 7 and the reference potential.
  • the inputs to the impedance converters 8 and 9 can contain bias resistors. This, however, leads to the result that saturation will not occur if electrodes 4 or 5 become insulated, or if the grounding rings become insulated, or if leads 6 or 7 break.
  • the circuit will still recognize non-symmetrical electrode impedances, since as noted earlier, these lead to increased noise content on the signals of electrodes 4 and 5.
  • the circuit will also recognize a break in the leads 6 and 7 and a connection to the reference potential of leads 6 or 7 as well as a conductive path between the electrodes 4 and 5 and the reference potential.
  • the measurement signal is only measured during the time interval TM (see FIG. 3). As shown in FIG. 4, the signal can be continuously measured when a bipolar sinusoidal magnetic field is used.
  • the measurement time intervals TM are stretched to include the entire half period. If a diagnosis is desired, the diagnostic time intervals T2, T3 and T4 can replace the corresponding measurement time interval TM and a diagnosis, as described above, can be carried out. Naturally, the measurement signal is lost during the total diagnostic time interval TD.
  • the circuit can, especially in connection with the arrangements illustrated in FIGS. 1 and 2, be provided with a resistor 46 connected in series with the coils 2 and 3, across which a voltage proportional to the excitation current I ERR can be derived and connected by lead 45 to amplifier 47 and the amplified signal fed to an input of the multiplexer 18 over lead 48.
  • a resistor 46 connected in series with the coils 2 and 3, across which a voltage proportional to the excitation current I ERR can be derived and connected by lead 45 to amplifier 47 and the amplified signal fed to an input of the multiplexer 18 over lead 48.
  • the circuit design shown in FIG. 2 contains a switch 37 which selectively can connect lead 6 with lead 14 or the lead 14 over terminal 37a to the reference potential and the lead 6 over terminal 37b to a high frequency generator 38.
  • the high frequency generator 38 feeds electrode 4 in the latter case.
  • the output signal of amplifier 16 is connected by lead 41 to an input of a high pass filter 39, whose output is connected by lead 42 to the multiplexer 18. If the high frequency generator 38 is connected to electrode 4, it is possible for the microprocessor 22 to determine if the signal from the high frequency generator 38 is disturbed or not disturbed and thereby make a disturbance analysis.
  • the electrodes 4 and 5 can be determined if at least one of the electrodes 4 and 5 is covered with an insulating layer, or if a conductive path exists between at least one of the electrodes 4 and 5 and the reference potential, or if at least one of the leads 6 and 7 is broken, or if at least one of the leads 6 and 7 is conductively connected to the reference potential.
  • the output of the summing circuit 52 is also connected by lead 80 to a high pass filter 56 whose output is connected by lead 82 to demodulator 58.
  • the output of the demodulator 58 is connected by lead 84 to a threshold switch 60 whose output is connected by lead 86 to a second alarm transmitter Alarm 2.
  • the summing circuit 52 will produce an output signal if non-symmetries exist in the circuit ahead of the summing circuit 52.
  • non-symmetries for example can result from:
  • FIG. 7 The design shown in FIG. 7 is different from the design shown in FIG. 6 in that a high frequency signal U G is produced by a high frequency generator 62 which is connected by lead 90 to a matched high pass filter 64 and applied to lead 7 through lead 88.
  • the output of the band pass filter 64 is connected by lead 92 to a demodulator 66 which is connected by lead 94 to a threshold switch 68.
  • the output of the threshold switch 68 is connected by lead 96 to an alarm transmitter Alarm 3.
  • a disturbance can occur for example due to:
  • the circuit shown in FIG. 7 can also be combined with the circuit shown in FIG. 6 with one or both alarm transmitters.
  • the output leads 76,86,96 which are connected to the alarm transmitters Alarm 1, Alarm 2, and Alarm 3 can, as in the first and second designs, be connected to a microprocessor.
  • the microprocessor can evaluate the various signals and provide to a display and/or to a binary output an appropriate error message.
  • the described designs are essentially independent from the normal evaluation of the signals +U S , -U S and from the time function of the excitation current.
US07/906,507 1991-07-04 1992-06-30 Magnetic flowmeter with fault detection Expired - Fee Related US5370000A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE4122225A DE4122225A1 (de) 1991-07-04 1991-07-04 Schaltungsanordnung zur ermittlung von fehlern in einer magnetisch-induktiven durchflussmessanordnung
DE4122225 1991-07-04

Publications (1)

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US5370000A true US5370000A (en) 1994-12-06

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US07/906,507 Expired - Fee Related US5370000A (en) 1991-07-04 1992-06-30 Magnetic flowmeter with fault detection

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US (1) US5370000A (de)
EP (1) EP0521448B2 (de)
JP (1) JP3199460B2 (de)
CA (1) CA2073130C (de)
DE (2) DE4122225A1 (de)
DK (1) DK0521448T4 (de)

Cited By (21)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5646353A (en) * 1995-10-20 1997-07-08 Endress + Hauser Flowtec Ag Electromagnetic flowmeter for measuring non-newtonian fluids
EP0915324A2 (de) 1997-11-04 1999-05-12 The Foxboro Company Magnetischer Durchflussmesser
US5907103A (en) * 1996-06-20 1999-05-25 Endress + Hauser Flowtec Ag Instrumentation amplifier arrangements of electromagnetic flowmeters
US5932812A (en) * 1995-05-22 1999-08-03 Delsing; Jerker Method and devices use in flow measurement
EP1108988A1 (de) * 1999-12-15 2001-06-20 Endress + Hauser Flowtec AG Verfahren und Vorrichtung zur Bestimmung der Durchflussrate eines Mediums in einem Messrohr
GB2371869A (en) * 2001-01-31 2002-08-07 Abb Automation Ltd Flowmeter fault detection
US6611770B1 (en) 1998-12-10 2003-08-26 Rosemount Inc. Liquid conduction indication in a magnetic flowmeter
WO2005012842A1 (de) * 2003-07-30 2005-02-10 Endress + Hauser Flowtec Ag Verfahren zur magnetisch-induktiven bestimmung der durchflussrate eines mediums
US20050087336A1 (en) * 2003-10-24 2005-04-28 Surjaatmadja Jim B. Orbital downhole separator
EP1584902A1 (de) * 2004-04-08 2005-10-12 Krohne Messtechnik Gmbh & Co. Kg Magnetisch-induktives Durchflussmessgerät und Verfahren zum Betreiben eines magnetisch-induktiven Durchflussmessgeräts
US20060000762A1 (en) * 2004-07-01 2006-01-05 Syed Hamid Fluid separator with smart surface
US20060037746A1 (en) * 2004-08-23 2006-02-23 Wright Adam D Downhole oil and water separator and method
EP1275940A3 (de) * 2001-07-09 2006-06-07 Endress + Hauser Flowtec AG Verfahren zum Betrieb eines magnetischinduktiven Durchflussmessers
US20070156354A1 (en) * 2004-01-17 2007-07-05 Ralf Backer Method for the operation of a flow measurement system
US20080258736A1 (en) * 2007-04-19 2008-10-23 Schulz Robert K Magnetic flowmeter output verification
WO2010121631A1 (en) 2009-04-22 2010-10-28 Siemens Aktiengesellschaft Electromagnetic flowmeter and method of operation thereof
WO2010132328A3 (en) * 2009-05-12 2011-01-06 Rosemount Inc. System to detect poor process ground connections within an electromagnetic flowmeter
USRE45447E1 (en) 2001-07-09 2015-04-07 Endress + Hauser Flowtec Ag Method of operating an electromagnetic flowmeter
US20160056816A1 (en) * 2014-08-21 2016-02-25 Spansion Llc Switching circuit
WO2017000214A1 (en) * 2015-06-30 2017-01-05 Rosemount Inc. Magnetic flowmeter with automatic in-situ self-cleaning
EP1285235B1 (de) * 2000-05-23 2017-03-08 Micro Motion, Inc. Elektromagnetischer durchflussmesser

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Publication number Priority date Publication date Assignee Title
US5426984A (en) * 1993-09-02 1995-06-27 Rosemount Inc. Magnetic flowmeter with empty pipe detector
JP3602636B2 (ja) * 1996-02-26 2004-12-15 愛知時計電機株式会社 電磁流量計
EP0814324B1 (de) * 1996-06-20 1999-08-18 Endress + Hauser Flowtec AG Messverstärker-Anordnungen von magnetisch-induktiven Durchflussmessern
DE10064738B4 (de) 2000-12-22 2004-02-12 Krohne Meßtechnik GmbH & Co KG Verfahren zur Prüfung eines magnetisch-induktiven Durchflußmeßgeräts
DE10118003A1 (de) * 2001-04-10 2002-10-24 Krohne Messtechnik Kg Magnetisch-induktives Durchflußmeßgerät und magnetisch-induktives Durchflußmeßverfahren
US6834555B2 (en) 2002-03-28 2004-12-28 Krohne Messtechnik Gmbh & Co. Kg Magnetoinductive flow measuring method
DE10256103B4 (de) * 2002-05-14 2004-09-16 Krohne Meßtechnik GmbH & Co KG Verfahren zur Bestimmung der Unsicherheit eines mit einer Meßfrequenz arbeitenden Meßverfahrens
DE10345297B4 (de) * 2003-09-30 2006-06-08 Abb Patent Gmbh Verfahren zum Betrieb einer induktiven Durchflussmesseinrichtung
DE10356008B4 (de) * 2003-11-27 2010-04-08 Krohne Meßtechnik GmbH & Co KG Verfahren zum Betreiben eines Meßgeräts
DE102007015368A1 (de) * 2007-03-28 2008-10-02 Endress + Hauser Flowtec Ag Verfahren zum Betreiben eines magnetisch-induktiven Durchflußmeßgeräts
DE102009045904A1 (de) 2009-10-21 2011-04-28 Endress + Hauser Flowtec Ag Magnetisch-induktive Durchflussmesseinrichtung und Verfahren zum Betreiben derselben
JP5439325B2 (ja) * 2010-09-27 2014-03-12 横河電子機器株式会社 電磁ログセンサ

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US4167871A (en) * 1978-06-02 1979-09-18 Fischer & Porter Co. Bi-directional electromagnetic flowmeter
US4676112A (en) * 1985-03-08 1987-06-30 Hitachi, Ltd. Electromagnetic flow meter
US4704908A (en) * 1985-10-23 1987-11-10 Flowtec Ag Method for compensating interference voltages in the electrode circuit in magnetic-inductive flow measurement
US4709583A (en) * 1985-10-31 1987-12-01 Sereg Electromagnetic flow meter using a pulsed magnetic field

Cited By (44)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5932812A (en) * 1995-05-22 1999-08-03 Delsing; Jerker Method and devices use in flow measurement
US5646353A (en) * 1995-10-20 1997-07-08 Endress + Hauser Flowtec Ag Electromagnetic flowmeter for measuring non-newtonian fluids
US6014902A (en) * 1995-12-28 2000-01-18 The Foxboro Company Magnetic flowmeter with diagnostics
US5907103A (en) * 1996-06-20 1999-05-25 Endress + Hauser Flowtec Ag Instrumentation amplifier arrangements of electromagnetic flowmeters
EP0915324A2 (de) 1997-11-04 1999-05-12 The Foxboro Company Magnetischer Durchflussmesser
EP0915324A3 (de) * 1997-11-04 1999-06-30 The Foxboro Company Magnetischer Durchflussmesser
US6611770B1 (en) 1998-12-10 2003-08-26 Rosemount Inc. Liquid conduction indication in a magnetic flowmeter
EP1108988A1 (de) * 1999-12-15 2001-06-20 Endress + Hauser Flowtec AG Verfahren und Vorrichtung zur Bestimmung der Durchflussrate eines Mediums in einem Messrohr
EP1285235B1 (de) * 2000-05-23 2017-03-08 Micro Motion, Inc. Elektromagnetischer durchflussmesser
US20020117009A1 (en) * 2001-01-31 2002-08-29 Ray Keech Flowmeter fault detection
US6843137B2 (en) 2001-01-31 2005-01-18 Abb Limited Flowmeter fault detection
GB2371869B (en) * 2001-01-31 2005-10-05 Abb Automation Ltd Flowmeter fault detection
GB2371869A (en) * 2001-01-31 2002-08-07 Abb Automation Ltd Flowmeter fault detection
AU783556B2 (en) * 2001-01-31 2005-11-10 Abb Limited Flowmeter fault detection
EP1275940A3 (de) * 2001-07-09 2006-06-07 Endress + Hauser Flowtec AG Verfahren zum Betrieb eines magnetischinduktiven Durchflussmessers
USRE45447E1 (en) 2001-07-09 2015-04-07 Endress + Hauser Flowtec Ag Method of operating an electromagnetic flowmeter
CN100420920C (zh) * 2003-07-30 2008-09-24 恩德斯+豪斯流量技术股份有限公司 用于磁感应确定介质流速的方法和装置
WO2005012842A1 (de) * 2003-07-30 2005-02-10 Endress + Hauser Flowtec Ag Verfahren zur magnetisch-induktiven bestimmung der durchflussrate eines mediums
US20070143041A1 (en) * 2003-07-30 2007-06-21 Endress + Hauser Flowtec Ag Method for magneto-inductive determination of the flow rate of a medium
US8757256B2 (en) 2003-10-24 2014-06-24 Halliburton Energy Services, Inc. Orbital downhole separator
US20050087336A1 (en) * 2003-10-24 2005-04-28 Surjaatmadja Jim B. Orbital downhole separator
US20070295506A1 (en) * 2003-10-24 2007-12-27 Halliburton Energy Services, Inc., A Delaware Corporation Orbital Downhole Separator
US20070156354A1 (en) * 2004-01-17 2007-07-05 Ralf Backer Method for the operation of a flow measurement system
EP1584902A1 (de) * 2004-04-08 2005-10-12 Krohne Messtechnik Gmbh & Co. Kg Magnetisch-induktives Durchflussmessgerät und Verfahren zum Betreiben eines magnetisch-induktiven Durchflussmessgeräts
US7462274B2 (en) 2004-07-01 2008-12-09 Halliburton Energy Services, Inc. Fluid separator with smart surface
US20090127179A1 (en) * 2004-07-01 2009-05-21 Halliburton Energy Services, Inc., A Delaware Corporation Fluid Separator With Smart Surface
US8211284B2 (en) 2004-07-01 2012-07-03 Halliburton Energy Services, Inc. Fluid separator with smart surface
US20060000762A1 (en) * 2004-07-01 2006-01-05 Syed Hamid Fluid separator with smart surface
US8449750B2 (en) 2004-07-01 2013-05-28 Halliburton Energy Services, Inc. Fluid separator with smart surface
US20060037746A1 (en) * 2004-08-23 2006-02-23 Wright Adam D Downhole oil and water separator and method
US7823635B2 (en) 2004-08-23 2010-11-02 Halliburton Energy Services, Inc. Downhole oil and water separator and method
US20080258736A1 (en) * 2007-04-19 2008-10-23 Schulz Robert K Magnetic flowmeter output verification
CN101688798B (zh) * 2007-04-19 2012-12-12 罗斯蒙德公司 磁流量计的输出校验
US7619418B2 (en) * 2007-04-19 2009-11-17 Rosemount Inc. Magnetic flowmeter output verification
WO2010121631A1 (en) 2009-04-22 2010-10-28 Siemens Aktiengesellschaft Electromagnetic flowmeter and method of operation thereof
CN102378901A (zh) * 2009-05-12 2012-03-14 罗斯蒙德公司 检测电磁流量计内较差的过程地线连接的系统
CN102378901B (zh) * 2009-05-12 2013-05-01 罗斯蒙德公司 检测电磁流量计内较差的过程地线连接的系统
US7921734B2 (en) 2009-05-12 2011-04-12 Rosemount Inc. System to detect poor process ground connections
WO2010132328A3 (en) * 2009-05-12 2011-01-06 Rosemount Inc. System to detect poor process ground connections within an electromagnetic flowmeter
US20160056816A1 (en) * 2014-08-21 2016-02-25 Spansion Llc Switching circuit
US9680465B2 (en) * 2014-08-21 2017-06-13 Cypress Semiconductor Corporation Switching circuit
WO2017000214A1 (en) * 2015-06-30 2017-01-05 Rosemount Inc. Magnetic flowmeter with automatic in-situ self-cleaning
CN106796130A (zh) * 2015-06-30 2017-05-31 罗斯蒙特公司 具有自动原位自清洁的磁流量计
US10746577B2 (en) 2015-06-30 2020-08-18 Micro Motion Inc. Magnetic flowmeter with automatic in-situ self-cleaning

Also Published As

Publication number Publication date
EP0521448B1 (de) 1999-03-17
DE4122225A1 (de) 1993-01-07
EP0521448A2 (de) 1993-01-07
JPH05187900A (ja) 1993-07-27
DK0521448T3 (da) 1999-10-11
JP3199460B2 (ja) 2001-08-20
DK0521448T4 (da) 2003-04-14
CA2073130A1 (en) 1993-01-05
EP0521448B2 (de) 2003-02-05
CA2073130C (en) 2002-01-01
EP0521448A3 (en) 1995-03-15
DE59209654D1 (de) 1999-04-22

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